Add GitHub action for PyPI releases

[julian-risch]

Is your feature request related to a problem? Please describe. Creating a PyPI release involves the same list of steps every time we have a new release. Manually going through these steps is error-prone and they could be automated instead

Describe the solution you'd like

1. Add a GitHub action that uses a GitHub secret (to be added) containing PyPI credentials and executes all steps necessary to release a new Haystack version.
2. Create a new branch for release preparations
3. Update version in haystack/VERSION.txt
4. Copy docs folder
5. Install Haystack from source with all dependencies pip install -e '.[all]'
6. Run .github/utils/generate_openapi_specs.py
7. Run .github/utils/generate_json_schema.py
8. Check plausability of schema updates
9. Push changes git push --follow-tags
10. Create git tag git tag -a vx.y.z -m "vx.y.z" and push
11. Run python3 -m pip install --upgrade build
12. Run python3 -m build
13. Check readme twine check dist/farm_haystack-x.y.z.tar.gz
14. Upload to PyPI twine upload dist/*
15. Test new release by installing from pip install farm-haystack==x.y.z

Describe alternatives you've considered Keep doing the releases manually is a bad alternative in my opinion because we rotate the responsibility of managing releases and a different environment would be used for every release.

Additional context A bonus would be slack integration that lets us know via slack about the successful release. 🎉